Friday 13 Mar 2020Nitride single photon sources

Rachel Oliver - University of Cambridge

Newman Red 12:30-12:30

Single photon sources are a key enabling technology for quantum communications, and are an important step towards more advanced quantum light sources with potential applications in other quantum information processing paradigms such as linear optical quantum computation.  In considering possible practical implementations of future quantum technologies, the nitride materials system is attractive since nitride quantum dots (QDs) achieve single photon emission at easily accessible temperatures, potentially enabling the implementation of quantum key distribution paradigms in contexts where cryogenic cooling is impracticable.

However, wurtzite nitride heterostructures grown along the polar c-axis typically exhibit large internal electric fields due to the polarisation mismatch between different alloys and to piezoelectric effects. Electrons and holes captured by a QD are separated by the field, reducing their probability of recombination and limiting the single photon source emission rate.  Whilst a number of approaches are being explored to overcome this issue, utilisation of nitride QDs grown on non-polar surfaces is particularly attractive since not only are the internal fields expected to be greatly reduced, but also the emission should be polarised along a specific crystal direction due to changes in the valence band structure induced by the asymmetric strain state of the material.

We have developed various methods for the formation of non-polar InGaN QDs utilising self-assembled growth regimes on either planar non-polar surfaces or the non-polar sidewalls of nanorod structures.  We demonstrate polarised single photon emission with short lifetimes from QDs grown by these various methods, and show that the properties of the QDs correlate well with the predictions of a model based on k.p theory.  The most successful QDs exhibit polarised optically-pumped single photon emission up to 220 K, a temperature accessible by on-chip cooling, and we have also demonstrated highly polarised electroluminescence from a single photon light emitting diode, and are developing cavity structures to increase the efficiency of single photon emission.

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